Atomic-Scale Measurement of Lattice Distortion in Sm-Doped Bismuth-Based Oxides

Element doping is an effective strategy to modulate the crystal structure and physical properties of layered oxides. In this work, atomic-resolution scanning transmission electron microscopy (STEM), combined with high-angle annular dark-field (HAADF) imaging and atomic-resolution energy-dispersive X-ray spectroscopy (EDS), was employed to systematically investigate Bi_1.85Sm_0.15O₃ (BSO) thin films prepared by spin-coating. The results show that Sm atoms preferentially occupy the second and fifth atomic layers within each six-layer unit, forming a long-range chemically ordered structure and generating a periodic built-in strain field. The periodic strain further induces local lattice distortion, with the distortion magnitude gradually increasing from approximately 4 pm near the substrate to 22 pm at the film surface. PFM measurements confirm that the films exhibit typical intrinsic ferroelectric characteristics, including butterfly-shaped amplitude loops, nearly 180° phase switching, and reversible domain switching behavior. This study reveals that doping-induced local lattice distortion serves as an important pathway for ferroelectric modulation in layered materials, providing atomic-scale structural insights for optimizing the ferroelectric properties of bismuth-based oxides.